Lens driving device, image stabilizing unit, and image pickup apparatus

ABSTRACT

A lens driving device having a simplified structure in which a holding member is moved relative to a stationary member with appropriate viscous damping is provided. The lens driving device includes the holding member configured to hold a compensation lens for image stabilization, the stationary member configured to support the holding member in a movable manner in a plane that is perpendicular to a light axis, a driving unit configured to change the position of the holding member relative to the stationary member, and a damping material disposed between the holding member and the stationary member. The damping material has a transition region in a frequency range between 0.3 Hz and 100 Hz.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 11/841,365, filed on Aug. 20, 2007, entitled “LENS DRIVINGDEVICE, IMAGE STABILIZING UNIT, AND IMAGE PICKUP APPARATUS”, the contentof which is expressly incorporated by reference herein in its entirety.This application also claims priority from Japanese Application No.2006-233122 filed Aug. 30, 2006, which is hereby incorporated byreference herein in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lens driving device for driving animage stabilizing lens, an image stabilizing unit including the lensdriving device, and an image pickup apparatus including the imagestabilizing unit.

2. Description of the Related Art

In recent years, with the advent of cameras with increasedfunctionality, many cameras have included an image stabilizing unit thatreduces image blur caused by vibration of the cameras. For example,Japanese Patent Laid-Open No. 60-143330 describes an image stabilizingunit that detects vibration, such as a camera shake, on the basis of agyro signal so as to stabilize an image by moving a part of an opticalsystem in a direction perpendicular to the light axis. This method hasbeen widely used.

It is desirable that a mechanism of image stabilization provides thefollowing two features: (a) small friction that allows excellenttrackability to be provided and (b) easy design of a frequencycharacteristic for designers. A variety of mechanisms have alreadyprovided these features.

For example, Japanese Patent Laid-Open No. 8-184870 describes amechanism including a lens driving device and a resilient unit and aviscous unit that restrict the displacement of a movable part. Such astructure can provide a mechanism that enables control known as “opencontrol” and an improvement of a frequency characteristic.

In addition, Japanese Patent Laid-Open No. 2001-290184 describes amechanism that includes a plurality of balls sandwiched by a supportmember that supports a compensation lens and a stationary member, andthe support member is urged by a resilient member. Such a structure candrive the support member using rolling friction, and therefore, canreduce a frictional force. Additionally, since a resonance frequency isdetermined by a ratio of the weight of the compensation lens and thesupport member to the elastic coefficient of the resilient member, adesired resonance frequency can be easily obtained. As a result,excellent controllability can be obtained so that the mechanism canappropriately respond to even a small vibration.

In addition, Japanese Patent Laid-Open No. 2-232824 describes amechanism in which a damping unit is attached to an actuator used for anoptical disc pickup. This mechanism is characterized in that appropriateportions of the mechanism are filled with a gel damping material servingas a damping unit. As a result, the improved frequency characteristic ofan apparatus can be provided with improved workability.

According to the technology described in Japanese Patent Laid-Open No.8-184870, a viscous resistance can be obtained using a mechanical orelectrical method. However, to obtain a viscous resistance through amechanical method, the structure is disadvantageously complicated and africtional force is disadvantageously increased. In contrast, to obtaina viscous resistance through an electrical method, the mechanismdisadvantageously has a negative impact from an assembly-to-assemblyvariation in an object to be controlled. In addition, the control systemdisadvantageously becomes complicated.

According to the technology described in Japanese Patent Laid-Open No.2001-290184, a compensation lens can be driven with a very smallfrictional force and can respond to a small camera shake. However, sincethis mechanism cannot provide an appropriate viscous resistance, themechanism is greatly affected by a primary resonance and asub-resonance, that is, the mechanism is easily affected by disturbance.

According to the technology described in Japanese Patent Laid-Open No.2-232824, the mechanism can easily obtain an appropriate viscousresistance. However, the structure is not always suitable for imagestabilizing units.

Therefore, it would be desirable to provide a lens driving device, animage stabilizing unit, and an image pickup apparatus having asimplified structure in which the location of a support member can bechanged relative to a stationary member with an appropriate viscousdamping.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a lens driving device, animage stabilizing unit, and an image pickup apparatus having asimplified structure in which the location of a support member can bechanged relative to a stationary member with an appropriate viscousdamping.

According to an embodiment of the present embodiment, a lens drivingdevice includes a holding member configured to hold a compensation lensfor image stabilization, a stationary member configured to support theholding member in a movable manner in a plane that is perpendicular to alight axis, a driving unit configured to change the position of theholding member relative to the stationary member, and a damping materialdisposed between the holding member and the stationary member. Thedamping material has a transition region in a frequency range between0.3 Hz and 100 Hz.

Further features and aspects of the present invention will becomeapparent from the following description of exemplary embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example structure of an image pickup apparatusaccording to various exemplary embodiments of the present invention.

FIG. 2 is a block diagram illustrating an exemplary electricalconfiguration of the image pickup apparatus shown in FIG. 1.

FIG. 3 is an exploded perspective view of a lens driving deviceaccording to a first exemplary embodiment of the present invention.

FIG. 4A is a front view of the lens driving device; while FIGS. 4B and4C are cross-sectional views of the lens driving device shown in FIG.4A.

FIGS. 5A and 5B are a plane view and a side view of an actuator includedin the lens driving device according to the first exemplary embodimentof the present invention, respectively.

FIG. 6A is a front view of a mounting portion of a damping unit includedin the lens driving device according to the first exemplary embodimentof the present invention; while FIGS. 6B and 6C are cross-sectionalviews of the mounting portion of the damping unit shown in FIG. 6A.

FIG. 7 is a frequency characteristic diagram of a viscoelastic materialaccording to the first exemplary embodiment of the present invention.

FIGS. 8A and 8B illustrate an analysis model of the lens driving deviceaccording to the first exemplary embodiment of the present invention.

FIG. 9 illustrates example values of various characteristics accordingto the first exemplary embodiment of the present invention.

FIG. 10 is a frequency-response diagram of the analysis model of thelens driving device according to the first exemplary embodiment of thepresent invention.

FIG. 11 is a schematic illustration of an experimental apparatus for thelens driving device according to the first exemplary embodiment of thepresent invention.

FIG. 12 illustrates experimental data of the frequency response of thelens driving device according to the first exemplary embodiment of thepresent invention.

FIG. 13 illustrates a frequency-response diagram of crosstalk of thelens driving device according to the first exemplary embodiment of thepresent invention.

FIG. 14 is a block diagram of a control signal processing system of thelens driving device according to the first exemplary embodiment of thepresent invention.

FIG. 15 illustrates a frequency-response diagram of a lens positioncontroller included in the control signal processing system shown inFIG. 14.

FIG. 16 is a frequency-response diagram illustrating frequency responsesbefore and after a phase compensator is applied to an image stabilizingunit according to the first exemplary embodiment of the presentinvention.

FIG. 17 illustrates a typical amplitude of a camera shake according tothe first exemplary embodiment of the present invention.

FIG. 18 is an exploded perspective view of an example lens drivingdevice according to a second exemplary embodiment of the presentinvention.

FIG. 19A is a front view of the lens driving device according to thesecond exemplary embodiment of the present invention; while FIGS. 19B to19D are cross-sectional views of the lens driving device shown in FIG.19A.

FIGS. 20A and 20B are a plan view and a side view of an actuatorincluded in the lens driving device according to the second exemplaryembodiment of the present invention, respectively.

FIG. 21 is a magnetic flux distribution diagram according to the secondexemplary embodiment of the present invention.

FIG. 22 is a block diagram of a control signal processing system of animage stabilizing unit according to the second exemplary embodiment ofthe present invention.

FIG. 23 is a block diagram illustrating feedback control performed bythe lens driving device according to the second exemplary embodiment ofthe present invention.

FIG. 24 is a frequency-response diagram of the feedback controlaccording to the second exemplary embodiment of the present invention.

FIG. 25 is a frequency-response diagram of a phase-lead compensatorincluded in the image stabilizing unit according to the second exemplaryembodiment of the present invention.

FIG. 26 is a frequency-response diagram of the feedback controlaccording to the second exemplary embodiment of the present invention.

FIG. 27 is a frequency-response diagram of the phase-lead compensatorincluded in the image stabilizing unit according to the second exemplaryembodiment of the present invention.

FIG. 28 is a frequency-response diagram of disturbance provided to thefeedback control according to the second exemplary embodiment of thepresent invention.

FIG. 29 is an exploded perspective view of an example lens drivingdevice according to a third exemplary embodiment of the presentinvention.

FIG. 30A is a front view of the lens driving device according to thethird exemplary embodiment of the present invention; while FIGS. 30B and30C are cross-sectional views of the lens driving device shown in FIG.30A.

FIGS. 31A and 31B are a plan view and a side view of an actuatorincluded in the lens driving device according to the third exemplaryembodiment of the present invention, respectively.

FIG. 32A is a front view of the lens driving device according to thethird exemplary embodiment of the present invention; while FIGS. 32B to32D are cross-sectional views of the lens driving device shown in FIG.32A.

FIG. 33 is an exploded perspective view of a lens driving deviceaccording to a fourth exemplary embodiment of the present invention.

FIG. 34A is a front view of the lens driving device according to thefourth exemplary embodiment of the present invention; while FIGS. 34Band 34C are cross-sectional views of the lens driving device shown inFIG. 34A.

FIGS. 35A to 35C illustrate the movement of a parallel link mechanism inthe lens driving device according to the third exemplary embodiment ofthe present invention.

FIGS. 36A and 36B are a plan view and a side view of an actuatorincluded in the lens driving device according to the fourth exemplaryembodiment of the present invention, respectively.

FIG. 37A is a front view of the lens driving device according to thefourth exemplary embodiment of the present invention; while FIGS. 37Band 37C are cross-sectional views of the lens driving device shown inFIG. 37A.

FIG. 38 illustrates a typical camera shake speed according to the fourthexemplary embodiment of the present invention.

DESCRIPTION OF THE EMBODIMENTS

Exemplary embodiments, features and aspects of the present invention aredescribed in detail below with reference to the accompanying drawings.

First Exemplary Embodiment

An image pickup apparatus according to a first exemplary embodiment ofthe present invention is described below with reference to FIGS. 1 to16. FIG. 1 illustrates an exemplary structure of the image pickupapparatus. In FIG. 1, an image pickup apparatus 1, an objective takinglens 2, and a lens driving device 3 that drives a compensation lens 12are shown. In addition, the objective taking lens 2 having a light axis4, a lens barrel 5, an image pickup element 6, a memory 7, a vibrationsensor 8 that detects a vibration, such as a camera shake, and a focuslens driving circuit 9 that drives a focus lens (not shown) incorporatedin the objective taking lens 2 are shown. A power supply 10, a releasebutton 11, the compensation lens 12, a quick-return mirror 13, and afinder optical system 14 are also shown. The lens driving device 3 andthe vibration sensor 8 form an image stabilizing unit.

The image pickup apparatus 1 forms an image on the image pickup element6 or in the vicinity of the image pickup element 6 using the objectivetaking lens 2 and a focus control unit (not shown). In addition, theimage pickup apparatus 1 acquires information about an object using theimage pickup element 6 and stores that information in the memory 7 insynchronization with a user's operation of the release button 11.

Image stabilization using the compensation lens 12 driven by the lensdriving device 3 is described next. The lens driving device 3 canappropriately drive the compensation lens 12. If camera shake occursduring exposure, a driving signal for stabilizing the image is generatedon the basis of a signal output from the vibration sensor 8. Thisdriving signal causes the lens driving device 3 to move the compensationlens 12 so that vibration of the image on the image pickup element 6 isreduced. Thus, reduction in the quality of the image due to camera shakecan be compensated for.

FIG. 2 is a block diagram illustrating an exemplary electricalconfiguration of the image pickup apparatus 1. The image pickupapparatus 1 includes an image pickup system, an image processing system,a recording and playback system, and a control system. The image pickupsystem includes the objective taking lens 2 and the image pickup element6. The image processing system includes an analog-to-digital (A/D)converter 20 and an image processing circuit 21. The recording andplayback system includes a recording processing circuit 23 and a memory24. The control system includes a camera system control circuit 25, anAF sensor 26, an AE sensor 27, the vibration sensor 8, an operationdetecting circuit 29, and a lens system control circuit 30. Also, theapparatus 1 includes a display unit 22 in communication with the camerasystem control circuit 25.

The image pickup system is an optical processing system that focuseslight output from an object on an imaging surface of the image pickupelement 6 so as to form an image on the imaging surface through theobjective taking lens 2. The image pickup system allows the image pickupelement 6 to be exposed with an object light beam having an appropriatelight intensity using an aperture (not shown) on the basis of a signaloutput from the AE sensor 27. The image processing circuit 21 includedin the image processing system processes image signals corresponding tothe number of pixels, the signals being received from the image pickupelement 6 via the A/D converter 20. The image processing circuit 21includes a white balance circuit, a gamma correction circuit, and aninterpolation computing circuit. The interpolation computing circuitincreases the resolution of the image through interpolation computation.The recording processing circuit 23 included in the recording andplayback system outputs an image signal to the memory 24. In addition,the recording processing circuit 23 generates and stores an image outputto a display unit 22. Furthermore, the recording processing circuit 23compresses a still image or a moving image using a predeterminedcompression method.

The control system controls components of the image pickup apparatus inresponse to a detection signal output from the operation detectingcircuit 29 that detects operations of the switches of the image pickupapparatus, such as the release button 11. The camera system controlcircuit 25 included in the control system generates timing signalsduring capturing an image and outputs the generated timing signals. TheAF sensor 26 detects a focusing state of the image pickup apparatus 1.The AE sensor 27 detects the luminance of the object. The vibrationsensor 8 detects vibration, such as a camera shake. The lens systemcontrol circuit 30 controls the focus lens driving circuit 9 and thelens driving device 3 in accordance with the signal output from thecamera system control circuit 25.

The control system controls the image pickup system, the imageprocessing system, and the recording and playback system in response toan external operation. For example, the control system detects that therelease button 11 is pressed and controls the drive of the image pickupelement 6, the operation of the image processing circuit 21, and thecompression process performed by the recording processing circuit 23. Inaddition, the control system controls each of segments of an informationdisplay unit, which displays various information on the optical finderand the liquid crystal monitor using the display unit 22.

The AF sensor 26 and the AE sensor 27 are connected to the camera systemcontrol circuit 25. The camera system control circuit 25 appropriatelycontrols the focus lens and an aperture via the lens system controlcircuit 30 on the basis of the signals from the AF sensor 26 and the AEsensor 27. In addition, the vibration sensor 8 is connected to thecamera system control circuit 25. In a mode in which image stabilizationis performed, the camera system control circuit 25 drives the lensdriving device 3 on the basis of a signal output from the vibrationsensor 8.

An image stabilizing process performed by changing an image scan area isdescribed next. According to the present exemplary embodiment, the scanarea of the A/D converter 20 can be changed in accordance with a signaloutput from the camera system control circuit 25. If camera shake occursduring exposure, the scan area is appropriately changed in accordancewith a signal output from the vibration sensor 8. In this way, even whenan object image is displaced on the image pickup element 6, asubstantially stationary object image can be obtained. Consequently, thevibration of an image delivered to the image processing circuit 21 canbe reduced, and therefore, the degradation in the quality of the imagecan be reduced.

If image stabilization performed by changing the image scan area andimage stabilization performed by driving the compensation lens 12 areimplemented and the two types of image stabilization operation work atthe same time, excess image stabilization is provided. Thus, an imagehas blurring in a direction opposite to a direction of input vibration.According to the technology described in Japanese Patent Laid-Open No.2-232824, image stabilizing units to be driven are switched inaccordance with the characteristic of an input signal so that anappropriate operation is obtained. According to the first exemplaryembodiment, the image stabilizing operation performed by moving thecompensation lens 12 sufficiently works and, concurrently, the simpleimage stabilization operation performed by changing the image scan areaappropriately works.

The lens driving device 3, which is part of the first exemplaryembodiment, is described next with reference to FIGS. 3 to 16.

FIG. 3 is an exploded perspective view of the lens driving device 3according to the present exemplary embodiment. As shown in FIG. 3, thelens driving device 3 includes a base plate 31, a movable lens barrel36, and ball bearings 32 a, 32 b, and 32 c sandwiched by the base plate31 and the movable lens barrel 36. The lens driving device 3 furtherincludes coils 33 a and 33 b, magnets 34 a and 34 b, elastic members 35a, 35 b, and 35 c, a magnet attraction plate 37, magnet attraction platefixing screws 38 a and 38 b, a movable lens barrel support plate 39, aflexible printed circuit board (FPC) 40, and FPC fixing screws 41 a and41 b.

As can be seen from FIG. 3, the lens driving device 3 according to thefirst exemplary embodiment can be expanded to one side of the base plate31. Thus, assembly of the lens driving device 3 is facilitated. As aresult, the productivity can be increased and the cost can be decreased.

FIGS. 4A to 4C illustrate the lens driving device 3 in detail. Morespecifically, FIG. 4A is a front view of the lens driving device 3 whenviewed in the light axis direction. FIG. 4B is a cross-sectional viewtaken along line IVB-IVB of FIG. 4A. FIG. 4C is a cross-sectional viewtaken along line IVC-IVC of FIG. 4A.

As shown in FIG. 4A, the movable lens barrel 36 is elastically supportedby the elastic members 35 a, 35 b, and 35 c on the base plate 31.According to the first exemplary embodiment, the elastic members 35 a,35 b, and 35 c radially extend from the light axis. The elastic members35 a, 35 b, and 35 c are spaced circumferentially at 120° intervals.This symmetric arrangement can prevent unwanted resonance excitationcaused by an occurrence of moment. In addition, as shown in FIG. 4C, theelastic members 35 a, 35 b, and 35 c are tilted in the light axisdirection at an appropriate angle and grasp the ball bearings 32 a, 32b, and 32 c disposed between the base plate 31 and the movable lensbarrel 36. A method for determining the elastic coefficients of theelastic members 35 a, 35 b, and 35 c is described later.

A relative movement between the base plate 31 and the movable lensbarrel 36 is described next with reference to FIGS. 3 and 4B. The ballbearings 32 a, 32 b, and 32 c are sandwiched by the base plate 31 andthe movable lens barrel 36 so that the base plate 31 moves relative tothe movable lens barrel 36 via the ball bearings 32 a, 32 b, and 32 c.Accordingly, the relative movement between the base plate 31 and themovable lens barrel 36 is affected only by a rolling friction. Since thefriction is small, the movement can be appropriately achieved in respondto a very small input. In addition, by manufacturing proper precisionsurfaces guided by the ball bearings 32 a, 32 b, and 32 c, aninclination of the movable lens barrel 36 and an unwanted movement ofthe movable lens barrel 36 in the light axis direction do not occur.

An actuator included in the lens driving device 3 is described next withreference to FIGS. 4C and 5A-B. As shown in FIG. 4C, the base plate 31has the coils 33 a and 33 b secured thereon whereas the movable lensbarrel 36 has the magnets 34 a and 34 b secured thereon. Thus, a movingmagnet actuator is formed. FIGS. 5A and 5B are schematic illustrationsof the actuator. FIG. 5A is a diagram of only the magnet 34 a and thecoil 33 a viewed in the light axis direction. FIG. 5B is across-sectional view of the magnet 34 a cut at substantially the centerof the magnet 34 a. The positional relationship between the magnet 34 band the coil 33 b is similar to that between the magnet 34 a and thecoil 33 a.

In FIGS. 5A and 5B, a magnetized boundary 43 between the N and S polesis shown. In FIG. 5B, magnetic field lines 42 a, 42 b, and 42 cschematically represent typical magnetic lines generated in thevicinities of the magnet 34 a and the coil 33 a. As shown in FIGS. 5Aand 5B, the magnet 34 a has two areas 34 a 1 and 34 a 2 with themagnetized boundary 43 therebetween. The two areas 34 a 1 and 34 a 2 aredifferently magnetized. The magnetized boundary 43 is oriented in adirection perpendicular to a direction of a force generated by theactuator. In FIG. 5A, the magnetized boundary 43 extends in an up-downdirection, and the magnet 34 a and the movable lens barrel 36 are movedin a left-right direction. The coil 33 a has an oval shape when viewedin the light axis direction. Two long portions 33 a 1 and 33 a 2 of thecoil 33 a face the areas 34 a 1 and 34 a 2 of the magnet 34 a,respectively.

As shown in FIG. 5B, the magnet attraction plate 37 is disposed on asurface of the magnet 34 a opposite the coil 33 a. It is desirable thatthe magnet attraction plate 37 is formed from a soft magnetic material.The magnet attraction plate 37 allows the majority of magnetic fluxes topass therethrough so as to decrease the permeance (the likelihood ofleakage) of a magnetic circuit. As a result, the magnetic field lines 42a and 42 b emanating from the magnet 34 a to the coil 33 a are linearlygenerated. According to the first exemplary embodiment, the magnetattraction plate 37 is secured to the movable lens barrel 36.Accordingly, as the thickness of the magnet attraction plate 37increases, the weight of the movable part increases. Therefore, it isdesirable that the magnet attraction plate 37 is located in the vicinityof saturated magnetic fluxes by considering the external shape of themagnet attraction plate 37, the saturation magnetic flux density, theshape of the magnet, and the surface magnetic flux density. In such astate, when the coil 33 a is energized, electric currents flow in thelong portions 33 a 1 and 33 a 2 in mutually opposite directions that areperpendicular to the plane of FIG. 5B. Accordingly, a driving forcegiven by the Fleming's left-hand rule is generated. As described in FIG.4A, since the movable lens barrel 36 is elastically supported, arelative movement between the base plate 31 and the movable lens barrel36 is caused until the base plate 31 and the movable lens barrel 36 aremoved to positions at which a resultant force of the elastic members 35a, 35 b, and 35 c matches the above-described driving force.

An exemplary method for mounting the damping unit providing a smallfriction and an optimum viscous resistance that allow acquisition of afrequency characteristic suitable for image stabilization is describednext with reference to FIGS. 6A to 6C. FIG. 6A is a front view of thelens driving device 3 when viewed in the light axis direction. FIG. 6Bis a cross-sectional view taken along line VIB-VIB of FIG. 6A. FIG. 6Cis a detailed diagram of the mounting portion of the damping unitsurrounded by a circle in FIG. 6B.

As shown in FIGS. 6A to 6C, the lens driving device 3 includes thedamping unit 45. The lens driving device 3 further includes mountingportions 44 a and 44 b of a damping unit 45. An arrow 46 indicates adirection in which an ultraviolet light beam is emitted. As shown inFIG. 6B, the magnet attraction plate fixing screws 38 a and 38 b areconnected to the movable lens barrel 36 and extend towards holes formedin the base plate 31 so as to overlap at least the base plate 31 in thelight axis direction. It is desirable that the mounting portions 44 aand 44 b are disposed at symmetric locations with respect to the lightaxis and a plurality of the mounting portions 44 a and 44 b aredisposed. According to the first exemplary embodiment, as shown in FIG.6B, the mounting portions 44 a and 44 b are disposed at symmetriclocations with respect to a light axis 4. The symmetric arrangement ofthe mounting portions 44 a and 44 b with respect to the light axis 4eliminates an occurrence of moment acting on the movable lens barrel 36due to a force exerted by the damping unit 45 when a relative movementbetween the base plate 31 and the movable lens barrel 36 occurs.

FIG. 6C is a detailed diagram of the mounting portion 44 a. The mountingportion 44 a is disposed so that a columnar shaft 38 a secured to themovable lens barrel 36 is substantially coaxial with a cylindrical holeformed in the base plate 31. The damping unit 45 is toroidal and isdisposed in a gap formed by the shaft 38 a and the inner surface of thehole. The damping unit 45 can be formed from one of a variety ofviscoelastic materials. According to the first exemplary embodiment, thedamping unit 45 is formed from a UV-curable silicon gel having excellentassemblability and resistance to environment. An opening is formed onone side of the unit. Accordingly, after uncured gel is applied to themounting portion 44 a, an ultraviolet light beam is emitted in adirection indicated by arrow 46 so as to cure the gel. A desiredcharacteristic of the viscoelastic material used for the damping unit 45is described later.

As shown in FIGS. 6A to 6C, let a denote a distance between a protrusionformed on the base plate 31 and a protrusion serving as a mechanicaloverrun prevention unit formed on the movable lens barrel 36, and “b”denotes a distance between the movable lens barrel 36 located at aposition at which the damping unit 45 is provided and the base plate 31serving as a fixed lens barrel, as shown in FIG. 6C. It is desirablethat the damping unit 45 is not significantly deformed and is used in arange in which no permanent deformations take place (i.e., a range inwhich the elastic coefficient linearly changes). Therefore, thefollowing condition is satisfied:a<b  (1)To avoid the occurrence of permanent deformation, it is desirable thatthe following condition is satisfied:a<0.5b  (2)

A desired characteristic of the viscoelastic material used for thedamping unit 45 is described next with reference to FIG. 7. In general,as shown in FIG. 7, the characteristic of a viscoelastic materialchanges in accordance with an input frequency. As is well known, aviscoelastic material has solid state properties for an increase infrequency similar to those for a decrease in temperature. That is, asshown in FIG. 7, a viscoelastic material has solid state properties ofrubber in a frequency region (hereinafter referred to as a “rubberregion”) 51 a lower than a transition region 51 b and has solid stateproperties of glass in a frequency region (hereinafter referred to as a“glass region”) 51 c higher than the transition region 51 b. In therubber region, a viscoelastic material is soft. However, in the glassregion, the viscoelastic material has Young's modulus 100 to 1000 timesthat in the rubber region.

The transition region 51 b is described next. In FIG. 7, f1 and f2represent a frequency that is sufficiently lower than an imagestabilization control frequency and a frequency that is sufficientlyhigher than the image stabilization control frequency, respectively. Leta range of about 1 sec to about 1/4000 sec be a practical shutter speedwhen an image is captured by the image pickup apparatus held by hand anda range of about 10 to about 400 mm (35 mm photography equivalent) be apractical focal length. Then, in general, the control frequency is setto a value in a range between about 0.3 Hz to about 100 Hz. In thepresent exemplary embodiment, the frequency f1 that is sufficientlylower than the control frequency is set to 0.001 Hz and the frequency f2that is sufficiently higher than the control frequency is set to 100000Hz. Values G1 and G2 represent the complex elastic modulus at thefrequency f1 and the complex elastic modulus at the frequency f2,respectively. Here, values G3 and G4 are defined using the values G1 andG2 as follows:G3=G1+0.1(G2−G1)  (3)G4=G1+0.9(G2−G1)  (4)

That is, the values G3 and G4 represent points having a 10% change fromeither end of the change width of the complex elastic modulus,respectively. According to the present exemplary embodiment, a regionbetween the values G3 and G4 is defined as the transition region 51 b.

In general, tan δ, which represents the ratio of the real part to theimaginary part of the complex elastic modulus, is increased in thetransition region 51 b located between the rubber region and the glassregion. Tan δ represents the hysteresis of a stress-distortion diagramof a viscoelastic material. As tan δ increases, the efficiency withwhich the kinetic energy is transformed to the thermal energy increases.Accordingly, as noted above, a material having the transition regionthat includes the control frequency region between 0.3 Hz and 100 Hz andhaving tan δ of a large value is desirable. In recent years, manymaterials that satisfy the above-described conditions have beendeveloped. A variety of products including a widely used butyl rubberhave been available.

The design of a driving system is described next with reference to FIGS.8A and 8B. FIGS. 8A and 8B are diagrams of a model of a movement of thedriving system according to the first exemplary embodiment. FIG. 8Aillustrates a model for the case when the damping unit is not presentwhereas FIG. 8B illustrates a model for the case when the damping unitis present.

According to the first exemplary embodiment, the lens driving device 3includes the three elastic members 35 a, 35 b, and 35 c. Whenconsidering a specific moving direction, the resultant force of theplurality of elastic members can be considered to be an imaginary springand an imaginary dash pod. As shown in FIG. 8A, the resultant force canbe represented by a one-degree-of-freedom spring-mass system. Adisplacement x associated with a given force F is expressed as follows:F=m(d2x/dt2)+c(dx/dt)+kx  (5)

At that time, as described in FIGS. 4A to 4C, the lens driving device 3is subjected to only a small friction. Accordingly, in general, theviscous resistance is small, and therefore, the value c is small. As aresult, this design generates strong resonance. That is, although thisdesign can appropriately respond to an input having a small amplitude,this design is easily affected by disturbance. Here, a damping ratio ξis defined as follows:ξ=c/(2√(mk))  (6)

The state at the resonance peak and the transient response of thespring-mass system can be obtained by using the damping ratio ξ. If thedamping ratio ξ is about 0.3 at about the resonance frequency, theexcellent controllability can be obtained. However, a widely usedmechanism having only a coil spring and having no damping units providesa damping ratio ξ of only about 0.1. Accordingly, since a mechanismhaving no damping units is easily affected by a resonance, the mechanismcan not always provide high controllability.

FIG. 8B illustrates a mechanism having a damping unit. That is, like theelastic members 35 a, 35 b, and 35 c, FIG. 8B illustrates a model inwhich the resultant force of a plurality of elastic members of thedamping unit 45 is considered to be an imaginary spring and a dash pod.In FIGS. 8B, k1 and c1 indicate a spring and a dash pod representingelastic members, respectively, and k2 and c2 indicate a spring and adash pod representing the damping unit, respectively. A relationshipbetween a displacement x and a given force F is expressed as follows:F=m(d2x/dt2)+(c1+c2)(dx/dt)+(k1+k2)x  (7)

When a suitable damping unit 45, as described in FIG. 7, is used, thevalue of tan δ is relatively large in the control range. If anappropriate material is used, tan δ of about 1.0 can be obtained. Inthis way, tan δ of a large value can be obtained. Accordingly, even whenk2 is small, a sufficient damping effect can be obtained. That is,appropriate damping can be provided without decreasing the sensitivityof the actuator. At that time, the damping ratio ξ is given by thefollowing equation:ξ=(c1+c2)/(2√(m(k1+k2)))  (8)

Frequency-response diagrams obtained through computation for the caseswhere the damping unit 45 is present and the damping unit 45 is notpresent under the condition illustrated in FIG. 9 are shown in FIG. 10.

FIG. 9 illustrates conditions for a mechanism suitable for a controlfrequency having an upper limit of about 30 Hz. In this model, the massof a movable part is set to 3 g. In addition, it is desirable that theresonance frequency is higher than the control frequency. In this model,the resonance frequency is set to 60 Hz. Furthermore, to increase thecontrol frequency in a so-called open control, it is desirable that theresonance frequency is further increased. As shown in FIG. 9, theelastic coefficient k1 of the resilient member and the elasticcoefficient k2 of the damping unit are determined while considering themass of the movable part, the control frequency, and a damping ratio ofthe whole mechanism. In FIG. 9, the unit is designed so that the dampingratio of the whole mechanism is 0.3. In general, as the elasticcoefficient k2 of the damping unit is increased, the damping ratio ofthe whole mechanism increases. However, as the elastic coefficient ofthe elastic member is decreased, a variation due to the weight of themechanism and disturbance increases. Therefore, the design is made whileconsidering these design points.

As can be seen from FIG. 10, when the damping unit is not present, aresonance peak noticeably appears. Therefore, the mechanism is easilyaffected by disturbance. In contrast, when the damping unit is present,the resonance is sufficiently prevented, and therefore, the mechanism isscarcely affected by disturbance. In addition, when the damping unit ispresent, the damping ratio is about 0.3, which is an appropriate value.As shown in FIG. 9, when the damping ratio is about 0.3, a rise in again caused by the resonance is small and the delay of the phase isrelatively small. In addition, to improve the controllability, the ratioof the elastic coefficient of the damping unit to that of the elasticmember can be determined so that the damping ratio is about 0.3.Furthermore, by changing the complex elastic modulus and the shape ofthe damping unit, the elastic coefficient of the damping unit can be setto a desired value.

Experimental data and the effects of the first exemplary embodiment aredescribed with reference to FIGS. 11 to 13. FIG. 11 is a schematicillustration of an experimental apparatus. A signal output from a fastFourier transform (FFT) analyzer 404 was applied to a coil via a motordriver 403 so as to drive the lens driving device 3. A response from thelens driving device 3 was measured using a laser displacement meter 401.The measured value was input to the FFT analyzer 404 via a laserdisplacement meter amplifier 402 so that the frequency response wasobtained.

FIG. 12 illustrates experimental data of the frequency response for thecases where a damping unit is present and a damping unit is not present.In the experiment shown in FIG. 12, a movable part and an elastic memberwere used so that the mass of the movable part was about 5 g and theresonance frequency was about 40 Hz. The damping unit was made fromTB3168 available from ThreeBond Co., Ltd. by appropriately curing TB3168using ultraviolet light. A neodymium magnet was partitioned into twoportions, each of which was magnetized. A soft magnetic material wasused for a magnet attraction plate. An adhesive polyurethane copper wirewas used for a coil. By applying an electrical current to the coil, adriving force is generated in proportion to the electrical current, andthe coil moves to a position at which a resultant force of the elasticmembers matches the driving force. At that time, it is desirable thatthe resultant force of the elastic members and the driving force do notgenerate a moment. However, a moment is generated due to, for example,an assembly-to-assembly variation. Thus, a rolling movement (hereinaftersimply referred to as “rolling”) about the light axis is produced. Asshown in FIG. 12, when the damping unit is not present, a resonance peak52 at about 40 Hz corresponds to a resonance in a direction of thedriving force. A resonance peak 53 at about 80 Hz corresponds to anunwanted resonance caused by the rolling. As can be seen from FIG. 12,since this mechanism has a small friction and a small viscousresistance, the resonance peaks 52 and 53 are high. In contrast, whenthe damping unit is present, any resonance peak does not appear even atabout 60 Hz at which the phase is delayed by 90 degrees. Accordingly,stable controllability can be provided. As can be seen, the gain and thephase vary in a frequency range higher than about 10 Hz. However, thisnegative impact can be reduced by a phase compensation unit, which isdescribed later.

FIG. 13 illustrates an experimentally obtained leakage (hereinafterreferred to as “crosstalk”) of the movement in one axis direction intoother axis directions. In a feedback control, some amounts of crosstalkare allowable since the crosstalk is corrected on the basis of a sensoroutput. However, in an open control, the crosstalk needs to be small.The crosstalk is caused by an assembly error of the elastic member andthe driving device, and therefore, it is difficult to completelyeliminate the crosstalk. In addition, when rolling is induced, crosstalknoticeably appears. As shown in FIG. 13, by providing a damping unit atan appropriate location, the rolling can be reduced, and therefore, thecrosstalk can be reduced. For example, the damping unit can be providedat a location at which a large velocity is induced when rolling occurs.According to the first exemplary embodiment, the damping unit isdisposed at a location separated from the light axis by a relativelylarge distance. Since the first exemplary embodiment can reduce thecrosstalk, the first exemplary embodiment is particularly effective forapparatuses using an open control.

An optimum control of the lens driving device 3 according to the firstexemplary embodiment is described next with reference to FIGS. 14 to 17.

FIG. 14 is a block diagram of a signal processing system for generatinga control signal of the lens driving device 3. In FIG. 14, an angularvelocity sensor 61, a lowpass filter (LPF) 62, and a central processingunit (CPU) 63 are shown. In addition, an A/D converter 64, an integrator65, a highpass filter (HPF) 66, and a memory 67 for recordinginformation about the image pickup apparatus are shown. Furthermore, alens position converter 68 for computing the position of the lens, alens position controller 69, a motor driver 70, and the lens drivingdevice 3 are shown.

As shown in FIG. 14, an angular velocity sensor is widely used for thevibration sensor 8 for detecting vibration, such as a camera shake. Thefirst exemplary embodiment is described with reference to the angularvelocity sensor 61. The angular velocity sensor 61 detects an angularvelocity caused by, for example, a camera shake and outputs a signal inproportion to the angular velocity. The LPF 62 generally removes noiseand, in particular, removes a high-frequency noise of the angularvelocity sensor 61. The CPU 63 performs computation required for controlof image stabilization. The CPU 63 includes the A/D converter 64, theintegrator 65, the HPF 66, the memory 67, the lens position converter68, and the lens position controller 69. The operations of thesecomponents are described in more detail next.

The A/D converter 64 converts a signal that has passed through the LPF62 to a digital signal at a predetermined sampling rate. It is desirablethat the sampling period is 100 times the control frequency range. Forexample, in the lens driving device 3 that controls a frequency lessthan or equal to 50 Hz, it is desirable that the A/D converter 64samples a signal at a sampling rate of about 5000 Hz. Thus, the effectof sampling is negligible. The integrator 65 integrates an angularvelocity signal so as to obtain an angle of a camera shake. The HPF 66removes a low-frequency fluctuation of the angular velocity sensor 61.The filter time constant is appropriately determined while consideringthe low-frequency fluctuation and the control frequency range. Inaddition, the HPF 66 can acquire shooting conditions, such as zoominformation, from the memory 67 so as to appropriately change the filtertime constant. The lens position converter 68 computes an amount ofmovement of the lens driving device 3 (more specifically, thecompensation lens 12) for the input vibration using information aboutzoom and focus stored in the memory 67. The lens position controller 69performs appropriate phase compensation while taking into considerationthe frequency characteristic of the lens driving device 3. In addition,the lens position controller 69 outputs the result of the process to themotor driver 70 so as to control the lens driving device 3.

FIG. 15 illustrates an example of the frequency response of a phasecompensator included in the lens position controller 69. This phasecompensator is a first-order phase-lead filter that reduces the load ofthe CPU 63. Accordingly, even a low-performance and relatively low-costCPU can be used. If the power of the CPU is so low that the CPU does notperform an additional process, the lens position controller 69 can besimply composed of a resistor and a capacitor outside the CPU. However,if the CPU has a sufficient power, a higher-order phase filter can beconfigured so that controllability higher than that described in thefirst exemplary embodiment can be provided.

FIG. 16 is a frequency response diagram illustrating the frequencyresponses before and after the phase compensator shown in FIG. 15 isprovided. As can be seen from FIG. 16, flat portions of the gain andphase continue to a high frequency region. This indicates that, even inan open control, the mechanism can compensate for a high-frequencycamera shake (vibration).

FIG. 17 illustrates a typical amplitude of the camera shake in thefrequency region. The ordinate represents a power spectrum correspondingto the amplitude of the vibration. The scale of the ordinate islogarithmic. Each scale mark denotes a value ten times larger than thepreceding one. As can be seen from FIG. 17, the amplitude of thevibration decreases towards higher frequencies. This indicates that theaffect of vibration of a high frequency is relatively smaller than thatof a low frequency. In addition, it is sufficient that the camera shakeis reduced during a time period determined by a shutter speed when astill image is captured and during a time period determined by a framerate when a moving image is captured. Accordingly, the effect of thevibration of a low frequency is relatively small. FIG. 17 alsoillustrates the amplitude of the vibration in the frequency under therestriction of 1/30 sec. A region in which the amplitude is large atthat time can be determined to be the control range. The shutter speedand the frame rate can be determined to be appropriate values inaccordance with the performance of the image pickup apparatus. In FIG.17, the control range is defined as a range between about 0.3 Hz andabout 20 Hz.

As for the mechanism shown in FIG. 17, the mechanism according to thefirst exemplary embodiment has a control range of a frequency less thanor equal to 100 Hz. An objective lens actuator of an optical disk has acontrol range of as high as several kHz. Since an actuator that shouldrespond in such a high frequency region needs to use a region close tothe glass region 51 c shown in FIG. 7, a viscoelastic material imposesload on the actuator. Accordingly, a viscoelastic material cannot bedirectly disposed between the movable part and the fixed part. However,according to the first exemplary embodiment, the control range islocated in a low-frequency range less than or equal to 100 Hz and thebandwidth is small. Accordingly, the transition region of a viscoelasticmaterial shown in FIG. 7 can be utilized.

A relationship between an amount of movement of the movable lens barreland the damping unit in a control state is described next. In theabove-described open control, the driving range may be electricallylimited due to the limitation of an electrical current. Let c denote anamount of movement of the movable lens barrel in the control state. Itis desirable that the damping unit 45 is not significantly deformed andis used in a range in which no permanent deformations take place (i.e.,a range in which the elastic coefficient linearly changes). Therefore,it is desirable that the following condition is satisfied:b>c  (9)where b represents the distance described in FIG. 6C. To avoid anoccurrence of permanent deformation, it is more desirable that thefollowing condition is satisfied:0.5b>c  (10)

As noted above, according to the first exemplary embodiment, the lensdriving device 3 can provide the following features:

1) Optimum damping in a mechanism having low friction

2) Easy assembly and low cost

3) Excellent control performance even under the open control.

Second Exemplary Embodiment

A second exemplary embodiment of the present invention is describedbelow with reference to FIGS. 18 to 28. Features of components of theimage pickup apparatus shown in FIGS. 1 and 2 have been described in thefirst exemplary embodiment. Therefore, descriptions are not repeated.

A lens driving device 3 which is a main component of the secondexemplary embodiment is described next with reference to FIGS. 18 to 28.FIG. 18 is an exploded perspective view of the lens driving device 3.Similar numbering will be used in describing FIG. 18 as was utilizedabove in describing the lens driving device 3 according to the firstexemplary embodiment. The lens driving device 3 includes a magnetattraction plate 101. The magnet attracting plate 101 is different fromthe magnet attraction plate 37 according to the first exemplaryembodiment in that the magnet attracting plate 101 has an appropriatehole. As can be seen from FIG. 18, a mechanism according to the secondexemplary embodiment can be expanded to one side of the base plate 31.Thus, the mechanism can be easily assembled. As a result, theproductivity can be increased and the cost can be decreased.

FIGS. 19A to 19D are diagrams illustrating the structure of the lensdriving device 3. More specifically, FIG. 19A is a front view of thelens driving device 3 when viewed in the light axis direction. FIG. 19Bis a cross-sectional view taken along line XIXB-XIXB of FIG. 19A. FIG.19C is a cross-sectional view taken along line XIXC-XIXC of FIG. 19A.FIG. 19D is a detail view of a damping unit mounting portion shown inFIG. 19C.

As shown in FIGS. 19A to 19D, a movable part is supported in a mannersimilar to that according to the first exemplary embodiment. That is, amovable lens barrel 36 is elastically supported by elastic members 35 a,35 b, and 35 c on the base plate 31. According to the second exemplaryembodiment, the three elastic members 35 a, 35 b, and 35 c radiallyextend from the light axis. The elastic members 35 a, 35 b, and 35 c arespaced circumferentially at 120° intervals. This symmetric arrangementcan prevent unwanted resonance excitation caused by an occurrence ofmoment. In addition, the elastic members 35 a, 35 b, and 35 c are tiltedin the light axis direction at an appropriate angle and grasp the balls32 a, 32 b, and 32 c disposed between the base plate 31 and the movablelens barrel 36. A method for determining the elastic coefficients of theelastic members 35 a, 35 b, and 35 c is described later.

The structure of the guide surface of the movable lens barrel 36 of thelens driving device 3 is similar to that shown in FIG. 4B according tothe first exemplary embodiment.

An actuator included in the lens driving device 3 is described next withreference to FIGS. 19B, 20 and 21. The actuator serves as a driving unitof the lens driving device 3. The actuator has a structure similar tothat shown in FIG. 4C. That is, by energizing coils 33 a and 33 b of theactuator, a relative movement occurs between the base plate 31 and themovable lens barrel 36. A difference between the actuators according tothe first and second exemplary embodiments is that the actuatoraccording to the second exemplary embodiment has a sensor 102 on theside of the surfaces of magnets 34 a and 34 b opposite the coils 33 aand 33 b. According to the second exemplary embodiment, the actuator isof a moving magnet type. Accordingly, a hall element is employed for thesensor 102. The sensor 102 is secured to the base plate 31 via an FPC40. The sensor 102 detects the position of the movable lens barrel 36using a change in the density of magnetic flux. In addition, bydisposing the sensor 102 at the above-described location, the magnet 34a for drive can be used for position detection.

FIGS. 20A and 20B are schematic illustrations of the actuator. FIG. 20Ais a view of the magnet 34 a, the coil 33 a, and the sensor 102 whenviewed in the light axis direction. FIG. 20B is a cross-sectional viewof the magnet 34 a when the magnet 34 a is cut at substantially thecenter thereof.

As shown in FIGS. 20A and 20B, the sensor 102 includes a magnetic fluxsensing portion 110. In a magnetic circuit shown in FIG. 20B, magneticfield lines 42 a, 42 b, and 42 c travels in directions indicated byarrows in FIG. 20B. In a state shown in FIG. 20B, the magnetic fluxsensing portion 110 is located immediately above a magnetized boundary43. Accordingly, the magnetic field at this point is substantially zero.When a relative movement between the base plate 31 and the movable lensbarrel 36 occurs, the magnetized boundary 43 is moved together with themovable lens barrel 36 from a viewpoint of the sensor 102 secured to thebase plate 31. Therefore, the magnetic field at the position of themagnetic flux sensing portion 110 is non-zero.

This operation is experimentally performed and the strength of themagnetic flux is shown in FIG. 21. In FIG. 21, a movement of zeroindicates the state in which the magnetic flux sensing portion 110 islocated immediately above the magnetized boundary 43, as shown in FIG.20B. As can be seen from FIG. 21, there is a linear relationship betweenthe amount of movement and the strength of a magnetic field in a certainrange. In this range, the position can be linearly determined.

A method for attaching the damping unit is described next with referenceto FIGS. 19C and 19D. As shown in FIGS. 19C and 19D, the lens drivingdevice 3 includes damping unit mounting portions 103 a and 103 b, adamping unit 104, and ultraviolet light-transparent plates 105 a and 105b. An arrow 106 indicates a direction in which an ultraviolet ray isirradiated. Like the first exemplary embodiment, the damping unitmounting portions 103 a and 103 b are disposed at symmetric locationswith respect to the light axis, as shown in FIG. 19C. FIG. 19D is anenlarged view of the damping unit mounting portion 103 a or 103 b. Asshown in FIG. 19D, magnet attraction plate fixing screws 38 a and 38 bare screwed to the movable lens barrel 36. Thereafter, each of themagnet attraction plate fixing screws 38 a and 38 b extends towards ahole formed in the base plate 31 so as to at least partially overlap thebase plate 31 in the light axis direction but so as not to passcompletely through to the other side of the hole. After the ultravioletlight-transparent plate 105 a is mounted on the base plate 31, thedamping unit 104 is poured. Thereafter, the movable lens barrel 36 isattached. Finally, the damping unit 104 is irradiated with anultraviolet light beam in a direction indicated by the arrow 106 so asto be cured. A viscoelastic material of the damping unit 104 is similarto that used for the first exemplary embodiment.

Optimal control of the lens driving device 3 according to the secondexemplary embodiment with reference to FIGS. 22 to 25.

FIG. 22 is a block diagram of a signal processing system for generatinga control signal of the lens driving device 3. Similar numbering will beused in describing FIG. 22 as was utilized above in describing the lensdriving device 3 shown in FIG. 14 according to the first exemplaryembodiment. The lens driving device 3 includes a lens position detectionsensor 111 and an A/D converter 112.

As shown in FIG. 22, a CPU 63 appropriately process a signal output froman angular velocity sensor 61, as in the first exemplary embodiment.According to the second exemplary embodiment, the lens positioncontroller 69 performs feedback control. Accordingly, the lens positioncontroller 69 controls the compensation lens using positionalinformation about the lens obtained through the lens position detectionsensor 111 and the A/D converter 112.

FIG. 23 is a block diagram illustrating the feedback control. In FIG.23, the term “target lens position” refers to a target position given bythe lens position converter 68. In addition, it is assumed that thesampling rate is one for sampling using a frequency sufficiently higherthan the control range. That is, the sampling does not cause a phasedelay. In FIG. 23, the sampling can be considered to be continuous. Inpractice, it is unnecessary that the lens driving device 3 used forimage stabilization provides a high-frequency response. Therefore, theassumption above is legitimate.

As shown in FIG. 23, let G2(s) denote a transfer function of the lensposition controller 69, Gd denote a driver gain of the motor driver 70,and G1(s) denote a transfer function of an actuator 113 of the lensdriving device 3, and Gs denote the gain of the lens position detectionsensor 111. Then, an open loop characteristic Gopen(s) is expressed asfollows:Gopen(s)=GdG1(s)G2(s)  (11)

Furthermore, a closed loop characteristic Gclose(s) is expressed asfollows:Gclose(s)=(GdGsG1(s)G2(s))/(1+GdGsG1(s)G2(s))  (12)The frequency-response diagrams at that time are shown in FIGS. 24 to27.

FIG. 24 illustrates the open loop characteristic (indicated by the term“OPEN”) and the closed loop characteristic (indicated by the term“CLOSE”) in the case where a damping unit is not employed. According tothe second exemplary embodiment, to simplify the control system, thelens position controller 69 is formed from a first-order phase-leadcompensator.

FIG. 25 is a frequency-response diagram of the phase-lead compensatorshown in FIG. 24. Even when the phase-lead compensator shown in FIG. 25is employed, it is difficult to sufficiently increase the crossoverfrequency when a phase margin is taken into account. In an example shownin FIG. 24, the crossover frequency appears at about 60 Hz and the phasemargin is about 30 deg. It is desirable that a region in which thephase-lead compensator advances the phase is in a lower frequency range.However, it is difficult because a spurious frequency appears at about80 Hz. Accordingly, the sensitivity at low frequencies cannot beincreased, and therefore, the crossover frequency cannot be increased.As the crossover frequency is increased, the phase margin is decreased.Consequently, the control system oscillates. Since the crossoverfrequency cannot be sufficiently increased, a phase delay occurs at lowfrequencies even in the closed loop characteristic. As a result, asufficient performance of the image stabilizing unit of the image pickupapparatus cannot be possibly obtained when the lens driving device isinstalled.

FIG. 26 illustrates the open loop characteristic (indicated by the term“OPEN”) and the closed loop characteristic (indicated by the term“CLOSE”) in the case where a damping unit is employed. FIG. 27 is afrequency-response diagram of the phase-lead compensator shown in FIG.26. When the phase-lead compensator, as shown in FIG. 27, is employed,the crossover frequency can be set at about 100 Hz. In addition, a phasemargin of about 45 deg. can be obtained, and therefore, a very stablecontrol system can be achieved. Since a high crossover frequency can beset, a phase delay can be prevented from a low frequency to a relativelyhigh frequency. According to the second exemplary embodiment, an optimumdesign of the open loop characteristic is made while taking into accountthis closed loop characteristic. That is, the elastic coefficient of theelastic member that supports the movable lens barrel 36 can beappropriately determined so as to obtain a desired resonance frequencyin the open loop characteristic.

As can be seen from the comparison between FIGS. 24 and 26, by employingthe optimum damping unit 104, the above-described desired characteristiccan be obtained even in an apparatus performing feedback control.

An adverse impact of disturbance is described with reference to FIGS. 23and 28. A transfer function Gnoise(s) from disturbance shown in a blockdiagram of FIG. 23 to an actual lens position can be expressed asfollows:Gnoise(s)=(GdG1(s))/(1+GdGsG1(s)G2(s))  (13)

A frequency-response diagram of this function is shown in FIG. 28. Ascan be seen from FIG. 28, when the damping unit 104 is employed, thegain for the disturbance at the actual lens position is smaller thanthat in the case when the damping unit 104 is not employed. Thus, theadverse impact of disturbance is small.

As noted above, according to the second exemplary embodiment, the lensdriving device 3 can provide the following features:

1) Optimum damping in a mechanism having low friction

2) Easy assembly and low cost

3) Stable control performance and prevention of a phase delay even underfeedback control.

Third Exemplary Embodiment

A third exemplary embodiment of the present invention is described belowwith reference to FIGS. 29 to 32. Features of components of the imagepickup apparatus shown in FIGS. 1 and 2 have been described in the firstexemplary embodiment. Therefore, descriptions are not repeated.

A lens driving device 3 which is a main component of the third exemplaryembodiment is described next with reference to FIGS. 29 to 32. FIG. 29is an exploded perspective view of the lens driving device 3.

Similar numbering will be used in describing FIG. 29 as was utilizedabove in describing similar components of the lens driving device 3according to the first exemplary embodiment. The lens driving device 3includes slide shafts 201 a, 201 b, and 201 c, a lock ring 202, a lockring drive motor 203, a rotation prevention bar 204, a fixed yoke 205,and a positioning reference pin 206. The lens driving device 3 furtherincludes screws 207 a, 207 b, 208, 212 a, 212 b, and 214, light emittingdiodes (LEDs) 209 a and 209 b, a counter yoke 210, a light shieldingplate 211, a relay FPC 213, and a photointerruptor 215.

Coils 33 a and 33 b and the LEDs 209 a and 209 b are secured to themovable lens barrel 36. Thus, the coils 33 a and 33 b and the LEDs 209 aand 209 b move together with the movable lens barrel 36. The relay FPC213 is secured to the base plate 31 by use of the screw 214. Electricalpower is supplied to the LEDs 209 a and 209 b, the photointerruptor 215,and the coils 33 a and 33 b via elastic portions on the relay FPC 213.

FIGS. 30A to 30C are plan views of the lens driving device 3. Morespecifically, FIG. 30A is a front view of the lens driving device 3 whenviewed in the light axis direction. FIG. 30B is a cross-sectional viewtaken along line XXXB-XXXB of FIG. 30A. FIG. 30C is a cross-sectionalview taken along line XXXC-XXXC of FIG. 30A.

As shown in FIGS. 29 and 30B, the slide shafts 201 a, 201 b, and 201 care fit to fitting holes formed in the base plate 31 and elongate holesformed in the movable lens barrel 36 so as to be secured to the baseplate 31. These three slide shafts and the three elongate holes guidethe movement of the movable lens barrel 36 in a plane perpendicular tothe light axis. The lock ring 202 is driven via a gear 216 coupled tothe lock ring drive motor 203. By rotating the lock ring 202, a state inwhich the lock ring 202 is in contact with the movable lens barrel 36and a state in which the lock ring 202 is not in contact with themovable lens barrel 36 can be switched. When the movable lens barrel 36is driven, the lock ring 202 is not in contact with the movable lensbarrel 36 so that an actuator, described below, can drive the movablelens barrel 36. In contrast, when, for example, the image pickupapparatus is powered off, the lock ring 202 is brought into contact withthe movable lens barrel 36 so that the movement of the movable lensbarrel 36 relative to the base plate 31 is restricted. Thephotointerruptor 215 can detect the movement of the lock ring 202. Therotation prevention bar 204 has an L shape. By providing appropriatecontact points to the rotation prevention bar 204, the rotationprevention bar 204 restricts the rotational movement of the movable lensbarrel 36 while allowing the movable lens barrel 36 to move togetherwith the base plate 31 in a plane perpendicular to the light axis.

The actuator in the lens driving device 3 is described next withreference to FIGS. 30C and 31. As shown in FIG. 29C, the fixed yoke 205,the counter yoke 210, and magnets 34 a 1 and 34 a 2 are secured to thebase plate 31. The coil 33 a is secured to the movable lens barrel 36.That is, a moving coil actuator is formed.

FIGS. 31A and 31B are schematic illustrations of the actuator. FIG. 31Ais a view of the magnets 34 a 1 and 34 a 2 when viewed in the light axisdirection. FIG. 31B is a cross-sectional view of the magnets 34 a 1 and34 a 2 when the magnet magnets 34 a 1 and 34 a 2 are cut atsubstantially the center thereof. As shown in FIG. 31A, the magnets 34 a1 and 34 a 2 are magnetized in opposite directions. In FIG. 31B,magnetic field lines 42 a, 42 b, and 42 c schematically representtypical magnetic lines generated in the vicinities of the magnets 34 a 1and 34 a 2 and the coil 33 a. The coil 33 a has an oval shape whenviewed in the light axis direction. Two long portions 33 a 1 and 33 a 2of the coil 33 a face the magnets 34 a 1 and 34 a 2, respectively.

As shown in FIG. 31B, the fixed yoke 205 is disposed on surfaces of themagnets 34 a 1 and 34 a 2 opposite the coil 33 a. It is desirable thatthe fixed yoke 205 is formed from a soft magnetic material. As shown inFIG. 31B, the fixed yoke 205 allows the majority of magnetic fluxes topass therethrough so as to decrease the permeance of a magnetic circuit.Furthermore, the counter yoke 210 is disposed on an opposite side of thecoil 33 a from the magnets 34 a 1 and 34 a 2, thus creating a closedmagnetic circuit. As a result, the magnetic field lines 42 a and 42 bemanating from the magnet 34 a to the coil 33 a are linearly generated.Since the fixed yoke 205 and the counter yoke 210 are secured to thebase plate 31, the thicknesses of the fixed yoke 205 and the counteryoke 210 can be freely determined so that the magnetic fluxes are notsaturated without concern for the weights thereof. In such a state, whenthe coil 33 a is energized, electric currents flow in the long portions33 a 1 and 33 a 2 in mutually opposite directions that are perpendicularto the plane of FIG. 31B. Accordingly, a driving force given by theFleming's left-hand rule is generated. As illustrated in FIG. 30B, sincethe movable lens barrel 36 is guided so as to move in a planeperpendicular to the light axis, the movable lens barrel 36 moves in theplane. By detecting the position of the movable lens barrel 36 using alens position sensor, described below, and performing feedback control,the movable lens barrel 36 can be moved to any position.

FIGS. 32A to 32D are plan views of the lens driving device 3. Morespecifically, FIG. 32A is a front view of the lens driving device 3 whenviewed in the light axis direction. FIG. 32B is a cross-sectional viewtaken along line XXXIIB-XXXIIB of FIG. 32A. FIG. 32C is across-sectional view taken along line XXXIIC-XXXIIC of FIG. 32A. FIG.32D is a detail view of a damping unit mounting portion 218 shown inFIG. 32C.

The lens position sensor is described next with reference to FIG. 32B.As shown in FIG. 32B, the lens position sensor includes an infraredlight emitting diode (LED) 209 a and a one-dimensional positionsensitive detector (PSD) 217 a secured to the base plate 31 via the FPC40. In the present exemplary embodiment, for simplicity, positiondetection in one axis direction is described. However, by using anadditional pair consisting of an LED and a one-dimensional PSD or byusing a two-dimensional PSD, position detection in two axis directionscan be performed. Electrical power is supplied to the LED 209 a via therelay FPC 213. The LED 209 a starts emitting light when imagestabilization starts. The one-dimensional PSD 217 a is implemented inthe FPC 40. Like the LED 209 a, electrical power is supplied to theone-dimensional PSD 217 a when image stabilization starts. Since amovement of the movable lens barrel 36 relative to the base plate 31changes the light intensity distribution on the one-dimensional PSD 217a, the position of the movable lens barrel 36 can be detected. Byperforming feedback control on the basis of a signal output from theone-dimensional PSD 217 a, as in the second exemplary embodiment, thelens position can be controlled so as to be changed to a desiredposition. In this way, image stabilization can be performed.

A method for mounting a damping unit is described next with reference toFIGS. 32C and 32D. In FIGS. 32C and 32D, the damping unit mountingportion 218 and a damping unit 219 are shown. FIG. 32D is an enlargedpartial detail view of the damping unit mounting portion 218 shown inFIG. 32C.

As illustrated in FIG. 30B, the slide shaft 201 a is fit to the elongatehole formed in the movable lens barrel 36. According to the thirdexemplary embodiment, a gap between the slide shaft 201 a and the innersurface of the elongate hole is filled with the damping unit 219. InFIGS. 32C and 32D, only part relating to the slide shaft 201 a isillustrated. However, gaps around the slide shafts 201 b and 201 c,which are not illustrated in FIGS. 32C and 32D, are also filled with thedamping unit 219. Thus, like the first and second exemplary embodiments,optimum damping can be obtained. In addition, according to the thirdexemplary embodiment, the damping unit 219 and the driving unit aredisposed in substantially the same plane. That is, the center line ofthe slide shaft 201 a (i.e., the center line of the damping unit 219)and the center line of the coils 33 a and 33 b (i.e., the center line ofthe driving force of the driving unit) are disposed in substantially thesame plane that is perpendicular to the light axis. Such an arrangementcan prevent unwanted yawing and pitching motions of the movable lensbarrel 36 caused by a force being applied by the damping unit 219.

As noted above, according to the third exemplary embodiment, the lensdriving device 3 can provide the following features:

1) Optimum damping

2) Prevention of unwanted yawing and pitching motions

3) Stable control performance and prevention of a phase delay even underfeedback control.

Fourth Exemplary Embodiment

A fourth exemplary embodiment of the present invention is describedbelow with reference to FIGS. 33 to 37A-C. Features of components of theimage pickup apparatus shown in FIGS. 1 and 2 have been described in thefirst exemplary embodiment. Therefore, descriptions are not repeated.

A lens driving device 3 which is a main component of the fourthexemplary embodiment is described next with reference to FIGS. 33 to37A-C.

FIG. 33 is an exploded perspective view of the lens driving device 3.Similar numbering will be used in describing components shown in FIG. 33as was utilized above in describing similar components of the imagestabilizing unit according to the first exemplary embodiment. The lensdriving device 3 includes elastic wires 301 a, 301 b, 301 c, and 301 d,fixed yokes 302 a and 302 b, and screws 303 a, 303 b, 303 c, 303 d, 307a, 307 b, 308 a and 308 b. The lens driving device 3 further includes afixed printed circuit board (PCB) 304, a movable PCB 305, and fixingpins 306 a and 306 b.

The fixed yokes 302 a and 302 b are secured to a base plate 31 by use ofthe screws 303 a, 303 b, 303 c, and 303 d. The fixed PCB 304 is securedto the base plate 31 by use of the screws 307 a and 307 b. The movablePCB 305 is secured to a movable lens barrel 36 by use of the screws 308a and 308 b. Magnets 334 a and 334 b are attracted to the fixed yokes302 a, and magnets 334 c and 334 d are attracted to the fixed 302 b sothat the magnets 334 a to 334 d are fixed to the base plate 31.

FIGS. 34A to 34C are plan views of the lens driving device 3. Morespecifically, FIG. 34A is a front view of the lens driving device 3 whenviewed in the light axis direction. FIG. 34B is a cross-sectional viewtaken along line XXXIVB-XXXIVB of FIG. 34A. FIG. 34C is across-sectional view taken along line XXXIVC-XXXIVC of FIG. 34A.

Main components of the lens driving device 3 according to the fourthexemplary embodiment are described next with reference to FIG. 33, FIG.34B, and FIGS. 35A-C. The movable lens barrel 36 is elasticallysupported by the base plate 31 via the elastic wires 301 a, 301 b, 301c, and 301 d. The elastic wires 301 a, 301 b, 301 c, and 301 d aresecured to the fixed PCB 304 and the movable PCB 305 by soldering. Thus,the elastic wires 301 a, 301 b, 301 c, and 301 d serve as elasticmembers so as to elastically support the movable lens barrel 36. Inaddition, the elastic wires 301 a, 301 b, 301 c, and 301 d serve as feedlines for feeding electrical power to the coils 33 a and 33 b.Phosphor-bronze wires or beryllium copper wires are suitably used forthe elastic wires 301 a, 301 b, 301 c, and 301 d. By disposing the fourwires having the same length substantially parallel to the light axis,the movable lens barrel 36 approximately functions as a parallel linkmechanism.

The movement of the parallel link mechanism is schematically illustratedin FIGS. 35A to 35C. As shown in FIGS. 35A to 35C, the elastic wires 301a, 301 b, 301 c, and 301 d are modeled as links 309 a and 309 b. Theelastic wires 301 a, 301 b, 301 c, and 301 d are bent so as to generatedisplacement. In FIGS. 35A to 35C, the displacement due to bendingdeformation is represented by the rotation of the links. It is assumedthat other deformation is not generated, and the links 309 a and 309 bare rigid bodies. As shown in FIGS. 35A to 35C, by forming the parallellink mechanism, the movable lens barrel 36 can be guided in a directionperpendicular to the light axis without generating an inclination of themovable lens barrel 36. In the parallel link mechanism, a movement inthe light axis direction occurs. Let x denote a movable range and ldenote the length of a wire. Then, the displacement in the light axisdirection is expressed as follows:l(1−cos(tan−1(x/l)))  (14)

For example, when the movable range is set to ±0.3 mm and the length ofthe wire is set to about 10 mm, the displacement in the light axisdirection is less than or equal to 5 μm. This value is within anallowable range. That is, the movable lens barrel 36 can be guided in aplane that is substantially perpendicular to the light axis without aninclination of the movable lens barrel 36.

An actuator of the lens driving device 3 is described next withreference to FIGS. 34C, 36A, and 36B. As shown in FIG. 34C, a coil fixedyoke 302 and the magnets 334 c and 334 d are secured to the base plate31 whereas the coil 33 b is secured to the movable lens barrel 36. Thus,a moving coil actuator is formed.

FIGS. 36A and 36B are schematic illustrations of the actuator. FIG. 36Ais a diagram of only the magnets 334 c and 334 d and the coil 33 aviewed in the light axis direction. FIG. 36B is a cross-sectional viewof the magnets 334 c and 334 d cut at substantially the center thereof.In FIG. 36A, a magnetized boundary 43 between the N and S poles isshown. In FIG. 36B, magnetic field lines 42 a, 42 b, 42 c, and 42 dschematically represent typical magnetic lines generated in thevicinities of the magnets 334 c and 334 d and the coil 33 a. As shown inFIG. 36A, the magnet 334 d has two areas 334 d 1 and 334 d 2 with themagnetized boundary 43 therebetween. The magnet 334 c has a similarconfiguration to that of the magnet 334 d. The coil 33 a has an ovalshape when viewed in the light axis direction. For example, two longportions 33 a 1 and 33 a 2 of the coil 33 a face the areas 334 d 1 and334 d 2 of the magnet 334 d, respectively.

As shown in FIG. 36B, the fixed yoke 302 b is disposed on a surface ofthe magnet 334 c opposite the coil 33 a. It is desirable that the fixedyoke 302 b is formed from a soft magnetic material. The fixed yoke 302 ballows the majority of magnetic fluxes to pass therethrough so as todecrease the permeance of a magnetic circuit. Furthermore, the fixedyoke 302 b is disposed on an opposite side of the magnet 334 d from thecoil 33 a. The magnets 334 c and 334 d are disposed so as to attracteach other. As a result, magnetic field lines 42 a and 42 b emanatingfrom the magnet 334 a to the coil 33 a are linearly generated. Accordingto the fourth exemplary embodiment, since the fixed yoke 302 b issecured to the base plate 31, the weight of a moving part does notchange even when the thickness of the fixed yoke 302 b is increased.Therefore, the thicknesses of the fixed yoke 302 b can be appropriatelydetermined so that the magnetic fluxes in the fixed yoke 302 b are notsaturated while taking into account the saturation magnetic fluxdensity, the shape of the magnet, and the surface magnetic flux density.In such a state, when the coil 33 a is energized, electric currents flowin the long portions 33 a 1 and 33 a 2 in mutually opposite directionsthat are perpendicular to the plane of FIG. 36B. Accordingly, a drivingforce given by the Fleming's left-hand rule is generated. As illustratedin FIGS. 34A to 34C, since the movable lens barrel 36 is elasticallysupported. Thus, a relative movement between the base plate 31 and themovable lens barrel 36 is caused until the base plate 31 and the movablelens barrel 36 are moved to positions at which a resultant force of theelastic wires 301 a, 301 b, 301 c, and 301 d matches the above-describeddriving force. Since the resultant force of the elastic wires 301 a, 301b, 301 c, and 301 d is proportional to an electric current forgenerating the driving force, the mechanism according to the fourthexemplary embodiment can be controlled using an open control method.

A method for mounting a damping unit is described next with reference toFIGS. 37A to 37C. FIG. 37A is a front view of the lens driving device 3when viewed in the light axis direction. FIG. 37B is a cross-sectionalview taken along line XXXVIIB-XXXVIIB of FIG. 37A. FIG. 37C is adetailed diagram of a damping unit mounting portion shown in FIG. 37B.In FIGS. 37B and 37C, the damping unit mounting portion 310 a, a dampingunit mounting portion 310 b, and a damping unit 311 are shown.

As shown in FIG. 37B, the fixing pins 306 a and 306 b are screwed to thebase plate 31. Thereafter, each of the fixing pins 306 a and 306 bextends towards a hole formed in the movable lens barrel 36 so as to atleast partially overlap the movable lens barrel 36 in the light axisdirection.

FIG. 37C is a detailed diagram of the damping unit mounting portion 310a. The damping unit mounting portion 310 a is disposed so that thecolumnar fixing pin 306 a secured to the base plate 31 is substantiallycoaxial with a cylindrical hole formed in the movable lens barrel 36.The damping unit 311 is toroidal and is disposed in a gap formed by thefixing pins 306 a and the inner surface of the hole. The damping unit311 can be suitably formed from the viscoelastic materials described inthe first exemplary embodiment. By using the above-described dampingunit 311, the same advantages as in the first exemplary embodiment canbe provided. In addition, according to the fourth exemplary embodiment,in order to facilitate the assembly, the fixing pins 306 a and 306 b areemployed. However, by changing the shape, the fixing pins 306 a and 306b can be produced in the form of structural objects on the base plate31.

Furthermore, according to the fourth exemplary embodiment, the dampingunit 311 and the driving unit are disposed in substantially the sameplane. That is, the center line of the damping unit 311 and the centerline of the coils 33 a and 33 b (i.e., the center line of the drivingforce of the driving unit) are disposed in substantially the same planethat is perpendicular to the light axis. Such an arrangement can preventunwanted yawing and pitching motions of the movable lens barrel 36caused by a force being applied by the damping unit 311.

FIG. 38 illustrates typical camera shake speeds in a frequency region.The ordinate represents speeds required for an image stabilizationmechanism corresponding to the angular velocity of the vibration. Thescale of the ordinate is logarithmic. Each scale mark denotes a valueten times larger than the preceding one. As can be seen from FIG. 17,the amplitude of the vibration decreases towards higher frequencies.Accordingly, as shown in FIG. 38, substantially the same speed caused bycamera shake is input even when the frequency varies. When a useroperates the image pickup apparatus to determine the composition ofpicture, an excessively high speed of camera shake is not input.

Therefore, according to the fourth exemplary embodiment, the mechanismlimits the control speed to 0.02 m/s, as shown in FIG. 38. A moving coilactuator, as used in the fourth exemplary embodiment, has a slightadvantage obtained by limiting the control speed. However, when, forexample, a stepping motor is used as a driving source, a possibility ofloss of synchronism can be advantageously reduced.

As noted above, according to the fourth exemplary embodiment, the lensdriving device 3 can provide the following features:

1) Optimum damping

2) Prevention of unwanted yawing and pitching motions

3) Stable control performance even under feedback control.

The features of the above-described exemplary embodiments are summarizedbelow.

1) The lens driving device 3 includes a fixed lens barrel, such as thebase plate 31, for holding the objective taking lens 2 that forms animage of an object, the movable lens barrel 36 for movably holding thecompensation lens 12 included in the objective taking lens 2 in a planeperpendicular to the light axis, one of an actuator for moving themovable lens barrel 36 relative to the fixed lens barrel in a frequencyregion less than or equal to 100 Hz (refer to the first to thirdexemplary embodiments) and an actuator for moving the movable lensbarrel 36 relative to the fixed lens barrel at a speed less than orequal to 0.02 m/s (refer to the fourth exemplary embodiment), and one ofthe damping units 45, 104, 219, and 311 disposed between the movablelens barrel 36 and the fixed lens barrel.

Such a structure can provide the lens driving device 3 with a simplifiedstructure, a small friction, an appropriate viscous resistance, and afrequency characteristic suitable for image stabilization for preventingcamera-shake blur.

2) The lens driving device 3 further includes a plurality of balls 32 ato 32 c sandwiched by the movable lens barrel 36 and the fixed lensbarrel and the elastic members 35 a, 35 b, and 35 c for urging themovable lens barrel 36 towards the fixed lens barrel. In place of theelastic members 35 a, 35 b, and 35 c, or in addition to the elasticmembers 35 a, 35 b, and 35 c, the lens driving device 3 may include aplurality of elastic wires 301 that extend parallel to the light axis ofthe objective taking lens 2 and that are secured to the movable lensbarrel 36 and the fixed lens barrel.

Such a structure can provide the lens driving device 3 with a furthersmall friction, thus responding to even a small vibration.

3) In the lens driving device 3, the damping unit and the actuator aredisposed in substantially the same plane that is substantiallyperpendicular to the light axis. In addition, a plurality of dampingunits are disposed at line-symmetric locations or point-symmetriclocations. Furthermore, the damping unit has a substantially circularshape when being projected onto a plane perpendicular to the light axis.Furthermore, the damping unit is disposed in a gap between the innersurface of a cylindrical hole formed in the movable lens barrel 36 and acolumnar shaft or between the inner surface of a cylindrical hole formedin the fixed lens barrel and a columnar shaft. Note that the cylindricalhole formed in the movable lens barrel 36 is not a through-hole.

Such a structure allows the lens driving device 3 to be insensitive tothe effect of a spurious resonance.

4) As shown in FIGS. 6A to 6C, let a denote a distance between a contactsurface of the movable lens barrel 36 and a contact surface of the fixedlens barrel for preventing the overrun of the movable lens barrel 36.Let b denote a distance between the movable lens barrel 36 located at aposition at which the damping unit is provided and the fixed lensbarrel. Then, the condition a<b is satisfied. More specifically, when adenotes a distance between a contact surface of the movable lens barrel36 and a contact surface of the fixed lens barrel for preventing theoverrun of the movable lens barrel 36, and b denotes a distance betweenthe movable lens barrel 36 located at a position at which the dampingunit is provided and the fixed lens barrel, the condition a<0.5b issatisfied. Alternatively, let b denote a distance between the movablelens barrel 36 located at a position at which the damping unit isprovided and the fixed lens barrel. Let c denote an amount of movementof the movable lens barrel in the control state. Then, the condition b>cis satisfied. More specifically, when b denotes a distance between themovable lens barrel 36 located at a position at which the damping unitis provided and the fixed lens barrel and c denotes an amount ofmovement of the movable lens barrel in the control state, the condition0.5b>c is satisfied.

Such a structure allows the lens driving device 3 to prevent anoccurrence of plastic deformation of the damping unit that provides aviscous resistance.

5) In the lens driving device 3, part of or all of the damping unit isin contact with the movable lens barrel 36 or the fixed lens barrel viaan ultraviolet light-transparent member. Such a structure allows thelens driving device 3 to be assembled with improve productivity.

6) In the lens driving device 3, the damping unit is formed from a gelthat consists primarily of silicon, an elastomer, or a butyl rubber.Such a structure allows the lens driving device 3 to have a damping unitformed from an optimum material.

7) In the lens driving device 3, the actuator is controlled by an opencontrol method. Such a structure allows the lens driving device 3 tohave a frequency characteristic suitable for image stabilization using asimplified structure.

As described above, by including the lens driving device 3 having anyone of the above-described structures, an image stabilizing unit and theimage pickup apparatus 1 having an excellent image stabilizationperformance and an excellent disturbance-proof performance can beachieved.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all modifications, equivalent structures and functions.

1. A lens driving device comprising: a holding member configured to holda compensation lens for image stabilization; a stationary memberconfigured to support the holding member in a movable mannersubstantially perpendicular to a light axis; a driving unit configuredto change the position of the holding member relative to the stationarymember; and a damping material disposed between the holding member andthe stationary member, wherein an axis member parallel to the light axisis provided to either of the holding member or the stationary member, ahole parallel to the light axis is provided to the holding member or theother stationary member, the axis member is inserted into the hole, andthe damping material is disposed between the axis member and the hole.2. The lens driving device according to claim 1, wherein the dampingmaterial is an ultraviolet-curable silicone gel and the gel material hasa transition region in the frequency range when the ultraviolet-curablesilicone gel is cured.
 3. The image stabilizing unit according to claim1, wherein the damping material is arranged in line symmetry or pointsymmetry when projected from the direction parallel to the light axis.4. The image stabilizing unit according to claim 1, wherein a shape ofthe hole is either round shape or oval figure when projected from thedirection parallel to the light axis.
 5. The image stabilizing unitaccording to claim 1, wherein the stationary member is having aregulation unit configured to regulate a motion of the holding member,and when defining movable range quantity between the hole and the axismember inserted to the hole as “b” and movable range quantity betweenthe holding member and the regulation unit of the stationary member as“a”, condition a<b is fulfilled.
 6. The image stabilizing unit accordingto claim 1, further comprising: a transparent member for transferringultraviolet light beam, wherein the transparent member contacts thedamping material and also contacts the stationary member or the holdingmember.
 7. The image stabilizing unit according to claim 1, wherein thedamping material and the driving unit are arranged in a same plane thatis perpendicular to a light axis.
 8. An image stabilizing unit whichincludes the lens driving device shown in claim
 1. 9. An image pickupapparatus having the image stabilization unit shown in claim
 8. 10. Animage stabilizing unit comprising: a holding member configured to hold acompensation lens for image stabilization; a stationary memberconfigured to support the holding member in a movable mannersubstantially perpendicular to a light axis; a driving unit configuredto change the position of the holding member relative to the stationarymember; a plurality of balls sandwiched between the holding member andthe driving unit; and a biasing member configured to bias the pluralityof balls to be sandwiched between the holding member and the drivingunit, one end of the biasing member is locked to the holding member andthe other end of the driving unit is locked to the stationary member,and a damping material disposed between the holding member and thestationary member, wherein an axis member parallel to the light axis isprovided to either of the holding member or the stationary member, ahole parallel to the light axis is provided to the holding member or theother stationary member, the axis member is inserted into the hole, andthe damping material is disposed between the axis member and the hole.11. The lens driving device according to claim 10, wherein the dampingmaterial is an ultraviolet-curable silicone gel and the gel material hasa transition region in the frequency range when the ultraviolet-curablesilicone gel is cured.
 12. The image stabilizing unit according to claim10, wherein the damping material is arranged in line symmetry or pointsymmetry when projected from the direction parallel to the light axis.13. The image stabilizing unit according to claim 10, wherein a shape ofthe hole is either round shape or oval figure when projected from thedirection parallel to the light axis.
 14. The image stabilizing unitaccording to claim 10, wherein the stationary member is having aregulation unit configured to regulate a motion of the holding member,and when defining movable range quantity between the hole and the axismember inserted to the hole as “b” and movable range quantity betweenthe holding member and the regulation unit of the stationary member as“a”, condition a<b is fulfilled.
 15. The image stabilizing unitaccording to claim 10, further comprising: a transparent member fortransferring ultraviolet light beam, wherein the transparent membercontacts the damping material and also contacts the stationary member orthe holding member.
 16. The image stabilizing unit according to claim10, wherein the damping material and the driving unit are arranged in asame plane that is perpendicular to a light axis.
 17. An image pickupapparatus which includes the image stabilizing unit shown in claim 10.